The arteries of the hand frequently vary from their usual mode of distribution.

Ordinarily there are, it will be remembered, two sets of arteries in the hand communicating with each other, viz., an ulnar or superficial set on the inner side, and a radial or deep set on the outer. Now, from the usual arrangement presented by these two sets of arteries there are numerous deviations, which may be classed as follows :

• By far the larger number of deviations consist of a deficiency in one or other of these sets of arteries, accompanied by a corresponding increase in the opposite one ; and it may be observed that the defect is much more commonly on the part of the superficial, and the increase on the part of the deep set.

• In a second and smaller class of variations a deficiency in one or other of the two systems above referred to is supplied, either by the enlargement of branches which descend in front of the limb, as the superficial volar (from the radial), or the median artery (from the anterior interosseous), or by the enlargement of a metacarpal branch (from the radial) on the back of the hand.

In illustration of these general remarks, the following modes of arrangement of the vessels may be mentioned.

In the greater number of cases the superficial palmar arch is diminished, and gives off fewer digital branches than usual. Generally only one branch is wanting, viz., that which supplies the adjacent sides of the fore and middle fingers ; but sometimes two or three branches are absent, or even all four, as when the ulnar artery, after giving branches to the short muscles of the little finger, ends in the deep palmar arch. In the last-named case, which is rare, it is obvious that the superficial arch is altogether wanting.

These various deficiencies in the superficial palmar arch and its branches are usually compensated for by an enlargement of the deep arch, the palmar inter-osseous branches of which, being increased in size, divide at the clefts of the fingers, and form such collateral digital branches as are not derived from the usual source. But a defective superfical arch may, as before mentioned, be reinforced from other vessels, viz., from the superficial volar, from an enlarged median artery, or from a large metacarpal branch.

It sometimes, but more rarely, happens, that the radial system of vessels is deficient ; in which case the superficial arch (which belongs to the ulnar system) may supply all the digital arteries to the thumb and fingers, or one of these may be derived from the superficial volar, the median, or the radial interosseous.

from Quain's Anatomy.